Stabilization is defined as protection of deterioration of the polymeric compositions during processing at high temperatures. This is needed in a number of applications to enhance resistance to thermal and light degradation and withstand more rigorous conditions. Stabilization in polymer compositions is typically achieved by incorporation of certain additive compounds. Broadly, these additives could be classified as phenolics (for example hindered phenolics) and non-phenolics (for example hydroxylamines, amine oxides, lactones, thioesters and phosphites). The non-phenolic stabilizers are disclosed in U.S. Pat. Nos. 4,403,053; 4,305,866 and 5,922,794, which discloses stabilization of polyolefins with a benzotriazole and a phosphite, a phosphite, and stabilization of polymers with tertiary amine oxide, based stabilizers respectively. U.S. Pat. No. 5,969,015 discloses monomeric or oligomeric bisphosphites as stabilizers for poly (vinyl chloride). The use of alkyl pentaerythritol phosphite as a thermal stabilizer for vinyl polymers has been disclosed in U.S. Pat. No. 6,362,260. U.S. Pat. No. 4,443,572 discloses stabilization of polyolefins with phosphites, hindered phenols and thioesters. These stabilizers do have some drawbacks. Stabilized polymer compositions containing certain phenolic antioxidants and hindered amine stabilizers tend to discolor upon storage. In addition these stabilizer could decompose and volatilize at high temperature and condensation of these volatile components as “fog” on the surface of the polymer composition. This is more prevalent with the presence of phenols.
Typically, phosphites are a class of secondary anti-oxidants and are often prone to hydrolysis. It is therefore important to have a high hydrolytic resistance. Good stabilizer should have a high thermal stability coupled with low volatility and high hydrolytic resistance. A preferred phosphite for use with mixed metal stabilizers is diphenyl isodecyl phosphite, but this generates phenol upon hydrolysis. Another stabilizer tris-(nonylphenyl) phosphite (hereinafter sometimes referred to by the abbreviation, “TNPP”) used along with tri-isopropanolamine to improve the hydrolytic stability for polyolefins.
There is a drive in polymer industry to have a non-phenol based material meeting the performance requirement of TNPP in polymers. There is also a need to develop alternate stabilizer that over come certain issues that phenolic stabilizers have as mentioned above. The known stabilizers do not satisfy all requirements with regard to factors, such as, shelf-life, water absorption, sensitivity to hydrolysis, and in-process stabilization. As a result, there continues to be a need for effective stabilizers for organic polymers. There is also a need to eliminate or minimize phenol content in the phosphite stabilizers and still have a stabilizer, which gives good color, hydrolytic and processing stability. Furthermore, it may be important to have a “green” or non-phenolic requirement while meeting the performance and cost criteria of the stabilizer and replace phenyl or substituted phenyl esters on a long term basis in the years to come.